Semi-permeable membranes are often used in separation applications to selectively allow passage of a purified material such as a fluid. For example, water filtration applications may use a filter to remove contaminants such as inorganic and organic particulate, bacteria, colloidal macromolecules, viruses, dissolved salts, and the like. Membrane technologies such as microfiltration, ultrafiltration, nanofiltration, and reverse osmosis, among others, may be used. These particular applications have seen tremendous growth in the United States in the recent past due to recent amendments to the Safe Water Drinking Act in 1996.
Because the primary role of the membrane is to act as a barrier to contaminants, it is essential that the integrity of the barrier be evaluated on a regular basis. Some methods and systems for evaluating membrane integrity are generally known. For example, it is known to apply a pressure differential across the membrane and measuring the time decay of the differential. The pressure differential may be applied using air, an inert gas, or vacuum, for example. These methods, however, require costly pressure tight enclosures, as well as systems for applying the elevated pressure or vacuum. Also, a continuous flow process using a membrane may have to be taken off line to perform testing.
Other methods for evaluating a membrane require regular testing of filtered fluid quality. When contaminants are discovered, the membrane is changed. Testing of the filtered fluid can be time consuming, costly, and may be limited in accuracy, however. For example, one system uses light scattering particle counters to detect the presence of contaminant particles, while other systems use electrical current/resistance measuring detectors or turbidity monitors. These systems and methods suffer a relatively low signal to noise ratio, and are generally limited by reasons of cost to detection of particles measuring >2 microns. Also, they are susceptible to false readings due to the presence of air bubbles, and are generally not suitable for detecting viruses.
Similar problems are associated with other known testing systems and methods, with the result that many problems remain unresolved in the art.